Enhanced cleaning for water-soluble flux soldering

ABSTRACT

An approach to provide an electronic assembly process that includes receiving at least one electronic assembly after a solder reflow process using a Sn-containing solder and a water-soluble flux. The approach includes baking the at least one electronic assembly in an oxygen containing environment and, then cleaning the at least one electronic assembly in an aqueous cleaning process.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of semiconductorpackaging processes and more particularly to cleaning processes forwater-soluble fluxes used in soldering of flip chip semiconductorpackaging and other electronic packages.

In the manufacture of integrated circuits, there is a continuing driveto fit more semiconductor devices and circuits in semiconductor wafersand electronic packaging assemblies, thus, driving denser, more complexsemiconductor packages such as flip chip semiconductor modules and ballgrid array (BGA) modules providing dense interconnection capability. Theassembly of flip chip semiconductor devices and BGA modules inelectronic packaging commonly involves the use of soldering processes.Fluxes play an important role is effective soldering processes byremoving surface oxides from solder and metal pad surfaces to enableeffective interconnection or solder joint formation during solderreflow.

Environmental concerns with previously used flux chemistries, such asrosin based fluxes or other fluxes that were cleaned after solderingusing halogenated hydrocarbons or fluorocarbons, have driven the use offluxes with a chemistry that is compatible with aqueous cleaningprocesses or mild, no clean fluxes that leave a non-conductive fluxresidue. Water-soluble fluxes generally provide a higher activity thanno clean fluxes and are required for some electronic assembly processes.Water-soluble fluxes are typically composed of one or more activators toremove surface oxides, solvents to aid in deploying flux to the solderjoint area, high temperature resistant chemicals, or vehicles that actas oxygen barriers and other additives (e.g., surfactants, thickeners,etc.). Water-soluble flux residues, if left after aqueous cleaning, maycause delamination of underfill from chip or substrate, and therefore,in most cases, it is desirable that water-soluble flux residues areremoved after solder reflow and assembly processes.

SUMMARY

Embodiments of the present invention provide a method for an electronicassembly process that includes receiving at least one electronicassembly after a solder reflow process using a Sn-containing solder anda water-soluble flux. The method includes baking the at least oneelectronic assembly in an oxygen containing environment and, thencleaning the at least one electronic assembly in an aqueous cleaningprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-section of a flip chip semiconductor module priorto aqueous cleaning in accordance with an embodiment of the presentinvention.

FIG. 2 depicts a portion of an assembly process flow for a flip chipsemiconductor module using a post solder reflow bake (PSRB) inaccordance with an embodiment of the present invention.

FIG. 3A depicts an example of a Sn-containing crystal formed fromwater-soluble flux residues after an aqueous clean in accordance with anembodiment of the present invention.

FIG. 3B is an example of a chart depicting the results of a post-aqueousclean semiconductor module inspection for Sn-containing crystals inaccordance with an embodiment of the present invention in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein. The method steps described below do not form a complete processflow for manufacturing semiconductor modules. The present embodimentscan be practiced in conjunction with the semiconductor packagingfabrication techniques and electronic packaging assembly techniquescurrently used in the art, and only so much of the commonly practicedprocess steps are included as are necessary for an understanding of thedescribed embodiments. The Figures represent cross-section portions of asemiconductor module or a semiconductor package during fabrication andare not drawn to scale, but instead are drawn to illustrate the featuresof the described embodiments. Specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. In thedescription, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

References in the specification to “one embodiment”, “other embodiment”,“another embodiment”, “an embodiment”, etc., indicate that theembodiment described may include a particular feature, structure orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is understood that it is within theknowledge of one skilled in the art to affect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing Figures. The terms “overlying”,“atop”, “over”, “on”, “positioned on” or “positioned atop” mean that afirst element is present on a second element wherein interveningelements, such as an interface structure, may be present between thefirst element and the second element. The term “direct contact” meansthat a first element and a second element are connected without anyintermediary conducting, insulating, or layers at the interface of thetwo elements.

In the interest of not obscuring the presentation of the embodiments ofthe present invention, in the following detailed description, some ofthe processing steps or operations that are known in the art may havebeen combined together for presentation and for illustration purposesand in some instances may not have been described in detail. In otherinstances, some processing steps or operations that are known may not bedescribed. It should be understood that the following description israther focused on the distinctive features or elements of the variousembodiments of the present invention.

Embodiments of the present invention recognize that water-soluble fluxcleaning processes may leave a flux residue, particularly in the case oflead-free flip chip assembly processes with high-densityinterconnections. High-density interconnections provide less space foraqueous cleaning solution entry and exit for flux removal after solderreflow. Additionally, embodiments of the present invention recognizethat common practices in industry may include solder reflow and bake ofsemiconductor packages and other electronic packaging assemblies innitrogen to avoid or reduce metal oxidation during solder reflow orbake. Furthermore, embodiments of the present invention recognize thatit is common practice in industry to minimize the time between solderreflow and a cleaning process to improve cleaning effectiveness and fluxresidue removal.

Embodiments of the present invention propose an addition of a postsolder reflow bake process in an oxygen-containing environment prior toan aqueous cleaning operation for electronic package assemblies andsemiconductor modules manufactured using a Sn-containing solder and awater-soluble flux. Embodiments of the present invention include a rangeof bake temperatures and bake times for the post solder reflow bake(PSRB) process to improve the effectiveness of an aqueous cleaningprocess in removing unwanted flux residues. Embodiments of the presentinvention propose that the PSRB process in an oxygen-containingenvironment is performed after solder reflow and prior to an aqueouscleaning operation to reduce or eliminate undesirable flux residues, andin particular, to eliminate the formation of Sn-containing crystalformed from water-soluble flux residues after aqueous cleaning.

As is known to one skilled in the art, fluxes can play an important rolein soldering operations and particularly in flip chip joining foradvanced semiconductor modules. As semiconductor chip size and I/Odensity for interconnects increase, the challenges for fluxes in formingacceptable solder joints during the solder reflow process may include anavoidance of post-soldering defect formation such as solder padnon-wets, post-solidification deformations (PSDs), and micro-solderballs, for example. The use of stronger, more active fluxes such aswater-soluble fluxes in high density advanced semiconductor packagesincluding flip chip semiconductor devices, ball grid array (BGA)packages, and high density PCB assemblies with BGA packages or otherlarge, densely configured I/O packages may reduce the occurrences ofpost-soldering defects. While improving yields by reducing theoccurrence of post-soldering defects during assembly and reflowprocesses, various water-soluble fluxes may leave flux residues that insome cases cannot be removed in typical aqueous cleaning operations.

While the discussion of embodiments of the present invention focuses onflip chip semiconductor device assembly processes, the method andprocesses discussed are not limited to flip chip semiconductor deviceassembly processes but can be applied to other water-soluble fluxelectronic assembly processes using a Sn-containing solder. For example,a PSRB process can be added to BGA module assembly processes usingwater-soluble fluxes or to any printed circuit board (PCB) assemblyprocess using a water-soluble flux with a Sn-containing solder and anaqueous cleaning process. In various embodiments, a PSRB process is usedin any suitable electronic packaging assembly process with one or moreSn-containing solders and a water-soluble flux after solder reflow andprior to aqueous cleaning to prevent the formation of Sn-containingcrystals, which are difficult to remove with an aqueous cleaningprocess.

FIG. 1 depicts a cross-section of a flip chip semiconductor module 100prior to solder reflow in accordance with an embodiment of the presentinvention. As depicted, FIG. 1 includes module substrate 101,water-soluble flux 102, solder interconnect 103, and flip chipsemiconductor device 105. In various embodiments, module substrate 101is any module substrate capable of supporting a solder interconnectionto a flip chip semiconductor device. For example, module substrate 101can be a laminate substrate, a ceramic substrate, a semiconductorsubstrate such as silicon, or other module substrate material used toattach a flip chip semiconductor device using a Sn-containing soldersuch as a lead-free solder. In some embodiments, module substrate 101 isa multichip module substrate capable of having more than onesemiconductor device attached as in a multichip module (MCM). In variousembodiments, module substrate 101 attaches to another level ofelectronic packaging (not shown in FIG. 1). For example, modulesubstrate 101 can be attached to a PCB by an interconnection such as asolder ball (e.g., a BGA module), a pin, a leadframe, a lead, or othertype of interconnection not shown in FIG. 1.

In various embodiments, water-soluble flux 102 can be any suitablewater-soluble flux for flip chip semiconductor device attached with asoldering process to a module substrate. For example, a water-solubleflux can be composed of at least one or more of the following componentsincluding an activator, a solvent, a vehicle, and additives. Activatorsfor a water-soluble flux include but are not limited to diacids such asoxalic acid, malonic acid, or glutaric acids, and multiacids such asdiethylenetriamine pentaacetic acid, tricarballylic acid, orbutanentetracarboxylic acid. Examples of solvents for water-soluble fluxinclude but, are not limited to isopropyl alcohol, glycol ethers,glycerol ethoxylates, alkyl diols, and epoxy resins. In otherembodiments, water-soluble flux 102 is a flux in another electronicpackaging assembly such as a BGA module assembly or a PCB assembly. Inan embodiment, water-soluble flux 102 is a set of one or more fluxesthat includes Indium® WS-3555. Water-soluble flux 102 can be a fluxapplied to either or both of module substrate 101 or flip chipsemiconductor device 105.

Solder interconnect 103 can be any suitable Sn-containing solderinterconnection formed during a solder reflow process with awater-soluble flux. For example, solder interconnect 103 can be formedfrom a reflowed plated solder bump, a reflowed solder ball, a reflowedscreened solder paste, a solder bump deposited by evaporation or othersimilar process on flip chip semiconductor device 105 or modulesubstrate 101. In various embodiments, solder interconnect 103 is formedfrom any Sn-containing solder. Examples of one or more Sn-containingsolders used to create solder interconnect 103 during a solder operationthat may use a PSRB process include lead-free solder compositions, Sn—Pbsolders, other lead-containing Sn-based solders, and any otherSn-containing solder for an electronic packaging assembly. In someembodiments, solder interconnect 103 is a lead-free flip chip solderinterconnection joining module substrate 101 to flip chip semiconductordevice 105.

FIG. 2 depicts a portion of an assembly process flow 200 for flip chipsemiconductor module 100 using a PSRB process in accordance with anembodiment of the present invention. In addition to depicting anassembly process flow that includes a PSRB process (Step 2) according toembodiments of the present invention, FIG. 2 includes a conventional orknown prior art process flow for a portion of a semiconductor moduleassembly process for a flip chip device attachment. The prior artprocess flow depicted in FIG. 2 includes an assembly process flowdepicted as Step 1 (solder reflow process) followed by Step 3 (aqueouscleaning process) and then, continues on to Step 4 which is thecontinuation to other downstream processes such as encapsulation,inspection, or test depending on the specific manufacturing process flowfor a module or a PCB assembly. As known to one skilled in the art, agoal in most traditional or prior art assembly process flows completedin manufacturing may be to minimize the time that occurs between Step 1and Step 3 to improve the effectiveness of an aqueous cleaning process(Step 3) by reducing flux residue residence time in the assembledmodule.

In various embodiments, as depicted in FIG. 2, an assembly process flowfor flip chip semiconductor device 105 attached to module substrate 101using a Sn-containing solder for solder interconnect 103 andwater-soluble flux 102 includes a PSRB process (Step 2). As depicted inFIG. 2, the assembly process flow for various embodiments of the presentinvention begins with Step 1 (solder reflow process) followed by Step 2,a PSRB process (i.e, a bake in air or other oxygen containingenvironment) then, proceeding to Step 3 (aqueous cleaning process), andon to Step 4 (the continuation to downstream processes). In variousembodiments, the addition of Step 2, a PSRB process reduces oreliminates the formation of Sn-containing crystals in the assembledmodule after the Step 3 aqueous cleaning process. As discussed in detailbelow, the addition of a treatment such as a PSRB process in air to theassembly process flow for a flip chip semiconductor module using aSn-containing lead free solder and a water soluble flux oxidizesundesirable Sn(II) carboxylate flux residues present after solder reflowto prevent the formation of difficult to remove Sn-containing crystalsformed by hydrolysis during a post soldering aqueous cleaning process.In the following discussions of Sn-containing carboxylate flux residues,II and IV in Sn(II) and Sn(IV) represent the oxidation states of Sn as+2 and +4, respectively. A more detailed description of each step in theassembly process flow in FIG. 2 is included below.

Step 1 is a solder reflow process for a Sn-containing solder using awater-soluble flux as known to one skilled in the art. In variousembodiments, the solder reflow process is for a lead-free solder used ina flip chip semiconductor module but is not limited to a flip chipsemiconductor reflow process. The lead-free solder may be any lead-freesolder containing Sn that is compatible with a flip chip semiconductormodule assembly process. For example, a lead-free solder may be a 98% Sn1.4% Ag 0.6% Cu with solder reflow peak temperatures in the range of 220degree Celsius to 270 degree Celsius. Other examples of a lead-freesolder that can be utilized in the PSRB process include but, are notlimited to various compositional ranges of Sn—Ag based solders, Sn—Ag—Cubased solders, Sn—Zn based solders, Sn—Sb based solders of variouscompositional ranges, any other lead-free solder that includes Sn, andany of the lead-free solders above that include an the addition of oneor more additional elements. In other embodiments, the solder reflowprocess with a water-soluble flux in Step 1 occurs using a lead basedsolder (e.g., Sn—Pb).

In Step 1, various water-soluble fluxes used in the solder reflowprocess may leave Sn-containing flux residue in addition to otherorganic and inorganic flux residue after solder reflow. Sn-containingflux residue may be observed as black dots that may be embedded in aviscous organic flux residue after solder reflow. Many typicalwater-soluble fluxes include one or more activators that may beactivators (R—(COOH)n) where R is an alkyl group or an alkyl-containinggroup. During Step 1 (solder reflow process) the activators react withvarious Sn oxides (SnO and SnO₂) present on solder pads or created atthe molten reflowed solder surface yielding R(COO)₂Sn(II) andR(COO)₄Sn(IV) respectively. By-products or Sn-containing flux residuesof the solder reflow process depicted in Step 1 for a solder processusing a water-soluble flux include a Sn(II) carboxylate, R—(COO)₂Sn(II),and a Sn(IV) carboxylate, R—(COO)₄Sn(IV).

As previously discussed, in the prior art process flow or a standardknown assembly processes depicted in FIG. 2, Step 3, an aqueous cleaningprocess follows Step 1, the solder reflow process with water-solubleflux. In this case according to known scientific processes, a Sn(II)carboxylate flux residue (i.e., R—(COO)₂Sn(II)) yielded during Step 1can form a cauliflower-like Sn-containing crystal as depicted in FIG. 3Aduring the next prior art step, Step 3 (aqueous cleaning process) uponhydrolysis. Based on scientific literature, the cauliflower-likeSn-containing crystals have a composition of either [Sn₃(OH)₄]²⁺ orSn₆O₄(OH)₄ as illustrated in the chemical equation below.

R(COO)₂Sn(II)+H₂O→[Sn₃(OH)₄]²⁺ or Sn₆O₄(OH)₄  Equation 1

In Equation 1 above, the resulting compounds which may be either[Sn₃(OH)₄]²⁺ or Sn₆O₄(OH)₄ can crystallize in an aqueous solution. TheSn-containing crystals created using the prior art process flow can beobserved on the surface of the semiconductor device or on the laminatemodule substrate surface after Step 3, the aqueous cleaning process, andthey are undesirable in an assembled module. The cauliflower-likeSn-containing crystals formed from Sn(II) carboxylates (water-solubleflux residues) after aqueous cleaning may be present on either one orboth of flip chip semiconductor device 105 and module substrate 101surfaces when using the prior art process flow depicted in FIG. 2 andmay not be removed with known aqueous cleaning processes in packed highdensity flip chip modules.

However, a Sn(IV) carboxylate flux residue also created in Step 1 doesnot crystallize easily upon its hydrolysis during the aqueous cleaningprocess in Step 3. A mixture of the Sn(IV) carboxylate flux residue andthe subsequently hydrolyzed by-products can be removed from the flipchip semiconductor module using known aqueous cleaning processes. Thehydrolysis of a Sn(IV) carboxylate occurs according to the chemicalequation below, Equation 2, where the formed Sn(IV)hydroxides are in anon-crystal form that dissolves in water and thus, are removed duringaqueous cleaning.

R(COO)₄Sn(IV)+H₂O→Sn(IV)hydroxides  Equation 2

After the completion of Step 1, a solder reflow process, in accordancewith embodiments of the present invention depicted in FIG. 2, a PSRBprocess (Step 2) is added to the assembly process flow as a post solderreflow bake in air or another oxygen-containing environment. A PSRBprocess is performed prior to the aqueous cleaning process (Step 3). APSRB process (Step 2) is a bake process in air that may be performedover a range of temperatures and a corresponding range of bake times. APSRB process of Step 2 is a method of oxidizing the Sn(II) component ofthe water-soluble flux residues, in particular Sn(II) carboxylate fluxresidues prior to cleaning (Step 3) the reflowed semiconductor module inwater. According to the chemical equation below, Equation 3, during aPSRB process, the Sn(II) carboxylate flux residues can react with oxygenin air to yield benign or non-crystallizing Sn(IV) carboxylate fluxresidues.

R(COO)₂Sn(II)+1/2O₂+R(COOH)₂→R(COO)₄Sn(IV)+H₂O  Equation 3

By oxidizing Sn(II) carboxylate flux residue into Sn(IV) carboxylateflux residue using the PSRB process of Step 2, the various embodimentsof the present invention provide a method to prevent the formation ofundesirable cauliflower-like Sn-containing crystals (e.g., created bythe hydrolysis of Sn(II) carboxylates during the aqueous cleaningprocess (Step 3). With the addition of a PSRB process in Step 2, theassembly process flow of FIG. 2 transforms or oxidizes the Sn(II)carboxylates into Sn(IV) carboxylates prior to aqueous cleaning andcreates R—(COO)₄Sn(IV) flux residues that, upon hydrolysis, do not yieldinsoluble crystals or adhere to the semiconductor device surface andmodule substrate surface (e.g., a laminate surface). Withoutcrystallization on the semiconductor device or on the laminate substratesurface, the Sn-containing flux residue created by hydrolysis of theSn(IV) carboxylates during the aqueous cleaning process (Step 3) may besuccessfully removed from the semiconductor module assembly (e.g., aflip chip semiconductor module) using known aqueous cleaning processes.In other embodiments, the PSRB process is performed before an aqueouscleaning process (Step 3) for any electronic packaging assembly processsuch as a BGA module assembly process or a PCB assembly process.

Upon completion of Step 3 (aqueous cleaning process), the assemblyprocess flow continues on to Step 4. Step 4 is the continuation ofdownstream processes such as module encapsulation, inspection, or testas determined by the type of module or electronic packaging assembly andthe manufacturing process for the electronic packaging assembly.

FIG. 3A depicts an example of a Sn-containing crystal 300 formed fromwater-soluble flux residues after an aqueous clean in accordance with anembodiment of the present invention. FIG. 3A depicts one example of acauliflower-like Sn-containing crystal. The Sn-containing crystal can beformed from Sn(II) carboxylates (water-soluble flux residues) afteraqueous cleaning of an electronic packaging assembly assembled using aSn-containing solder. In some embodiments, a PSRB process (Step 2 inFIG. 2) used with some water-soluble fluxes and an inadequate or too lowbake temperature or a too short bake time may result in the creation ofone or more Sn-containing crystals. A Sn-containing crystal, as depictedin FIG. 3A, may be formed from Sn(II) carboxylates (water-soluble fluxresidues) after aqueous cleaning of a flip chip module assembled using aSn-containing solder. Sn-containing crystals may also be formed when theelectronic assembly or semiconductor module is assembled with aSn-containing solder and a water-soluble flux without a PSRB process. ASn-containing crystal as depicted in FIG. 3A may be present on either orboth of the semiconductor device and module substrate surfaces after anassembly flow process (e.g., FIG. 2). While FIG. 3A depicts an exampleof a Sn-containing crystal, as known to one skilled in the art, somevariation may occur in the crystal structure of a Sn-containing crystalin other examples.

FIG. 3B is an example of a chart 350 depicting the results of apost-aqueous clean semiconductor module inspection for Sn-containingcrystals in accordance with an embodiment of the present invention. FIG.3B is a matrix of the results for a post water clean inspection ofsemiconductor modules assembled using assembly process flow 200 depictedin FIG. 2. The semiconductor modules inspected were assembled using aPSRB process that includes a range of bake temperatures combined with arange of bake times as depicted in the matrix of results in FIG. 3B. Thematrix identifies the number of semiconductor modules observed withSn-containing crystals on either the semiconductor device surface or thelaminate module substrate surface after performing Step 1, Step 2, andStep 3 in FIG. 2. FIG. 3B depicts the results for the number ofinspected semiconductor modules with one or more observed Sn-containingcrystals after cleaning for a range of bake temperatures in degreesCelsius (X axis) and for a range of associated bake time in minutes (Yaxis).

The results of the module inspection are represented in FIG. 3B as thenumber of semiconductor modules observed without Sn-containing crystalsout of the total number of semiconductor modules inspected using variousPSRB processes bake temperatures and bake times (e.g., 0/118 or zerosemiconductor modules observed with Sn-containing crystals for 118inspected semiconductor modules using a PSRB with a bake temperature of110° Celsius and a bake time of 70 minutes). The inspection results arepresented for a range of various bake temperatures (X axis) and a rangeof various bake times (Y axis). FIG. 3B illustrates that the addition ofa PSRB process for a range of different combinations of temperatureranging from 60° C. to 120° C. and bake time ranging from 30 minutes to180 minutes were effective in eliminating Sn-containing crystals aftersolder reflow, air bake (PSRB process), and a standard aqueous cleaningprocess.

While FIG. 3B depicts an example of post-aqueous clean semiconductormodule inspection for Sn-containing crystals in semiconductor modulesbaked with a PSRB process using various bake temperatures and baketimes, a PSRB process is not limited to the depicted bake temperaturesand bake times. For example, a PSRB process may use higher temperaturesthan shown in FIG. 3B such as 180° Celsius or above and may use lowertemperatures such as 40° Celsius. Additionally, the PSRB process mayinclude shorter bake times such as fifteen minutes associated withhigher temperatures (greater than 120° Celsius) or longer bake timesgreater than one hundred and eighty minutes (i.e., more than threehours) associated with lower temperatures (e.g., less than 60° Celsius).

In some embodiments, the flip chip semiconductor devices used by theembodiments of the present invention may be diced in semiconductor chipform or in diced semiconductor wafer form. The flip chip semiconductordevices may be mounted in a single chip package (such as a plasticcarrier depicted in FIG. 1, with a lead (not shown) that is affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic substrate, semiconductor or laminate substrate thathas either or both surface interconnections or buried interconnections).In any case, the semiconductor device is then integrated with otherchips, discreet circuit elements, motherboard or (b) end product for anelectronic assembly. The end product can be any product that includessemiconductor devices, ranging from toys and other low-end applicationsto advanced computer products having a display, a keyboard or otherinput device and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for an electronic assembly processcomprising: receiving at least one electronic assembly after a solderreflow process using a Sn-containing solder and a water-soluble flux;baking the at least one electronic assembly in an oxygen containingenvironment, and cleaning the at least one electronic assembly in anaqueous cleaning process.
 2. The method of claim 1, further comprisingbaking the at least one electronic assembly in the oxygen containingenvironment within a range of temperatures from 40° Celsius to 180°Celsius.
 3. The method of claim 1, further comprising baking the atleast one electronic assembly in the oxygen containing environment forat least one of 60° Celsius for thirty minutes and 120° Celsius forthree hours.
 4. The method of claim 1, further comprising baking the atleast one electronic assembly for a range of temperatures from 60°Celsius to 120° Celsius for a corresponding range of bake times fromthirty minutes to three hours.
 5. The method of claim 1, furthercomprising baking the at least one electronic assembly in an oxygencontaining environment for a time less than thirty minutes with a bakingtemperature more than 120° Celsius.
 6. The method of claim 1, furthercomprising baking the at least one electronic assembly in an oxygencontaining environment for a time more than one hundred and eightyminutes with a baking temperature less than 60° Celsius.
 7. The methodof claim 1, wherein the water-soluble flux is any suitable water-solubleflux used in an electronic packaging assembly.
 8. The method of claim 1,further comprises the water-soluble flux including at least one or moreof the following an activator, a solvent, a vehicle, and one or moreadditives.
 9. The method of claim 1, wherein the at least one electronicassembly includes using the solder reflow process for interconnectingone or more flip chip semiconductor devices to a module substrate. 10.The method of claim 1, wherein the at least one electronic assemblyincludes using the solder reflow process for a BGA module assemblyprocess.
 11. The method of claim 1, wherein the at least one electronicassembly includes using the solder reflow process in a printed circuitboard assembly.
 12. The method of claim 1, wherein the solder reflowprocess further comprises forming a solder interconnection from one ormore of a plated solder bump, a solder ball, a solder bump deposited byan evaporation process, and a solder paste.
 13. The method of claim 1,wherein receiving the at least one electronic assembly after solderreflow process includes receiving at least one of a flip chipsemiconductor device with a plurality of solder interconnections tomodule substrate, a BGA module, and an assembled printed circuit board.14. The method of claim 1, wherein the at least one electronic assemblyusing the Sn-containing solder includes using at least one of a Sn—Pbsolder, a lead-free solder, and other Sn-containing solder.
 15. Themethod of claim 1, wherein the solder reflow process using theSn-containing solder includes at least one of Sn—Ag based solders,Sn—Ag—Cu based solders, Sn—Zn based solders, and Sn—Sb based solders.16. The method of claim 1, wherein baking the at least one electronicassembly in an oxygen containing environment further comprises bakingthe at least one electronic assembly to oxidize Sn(II) carboxylate fluxresidue into Sn(IV) carboxylate flux residue.
 18. The method of claim17, wherein hydrolysis of Sn(IV) carboxylate flux residue during theaqueous cleaning process does not yield insoluble crystals.
 19. Themethod of claim 1, wherein receiving the at least one electronicassembly after a solder reflow process using a Sn-containing solder anda water-soluble flux further comprises: receiving the at least oneelectronic assembly that is a flip chip semiconductor module after thesolder reflow process using the Sn-containing solder that is a lead-freesolder and the water-soluble flux that is Indium® WS-3555.
 20. Themethod of claim 1, wherein baking the at least one electronic assemblyin an oxygen containing environment for a range of temperatures between60° Celsius and 120° Celsius improves the effectiveness of the aqueouscleaning process in removing undesirable flux residues.